New York: Can the world live without Wikipedia for a day? The shutdown of one of the Internet's most-visited sites is going down well with some of its volunteer editors, who say the protest of anti-piracy legislation could threaten the credibility of their work.

"My main concern is that it puts the organisation in the role of advocacy, and that's a slippery slope," said editor Robert Lawton, a Michigan computer consultant who would prefer that the encyclopedia stick to being a neutral repository of knowledge. "Before we know it, we're blacked out because we want to save the whales."

The protest is aimed at the Stop Online Piracy Act in the House of Representatives and the Protect Intellectual Property Act under consideration in the Senate. Both bills are designed to crack down on sales of pirated American products overseas, and they have the support of the film and music industry.

Among the opponents are many Internet companies such as Google, Facebook, Yahoo, Twitter, eBay and AOL. They say the bills would hurt the industry and infringe on free-speech rights.

Wikipedia's English-language site shut down at midnight Eastern Standard Time on Tuesday (0500 GMT Wednesday) and the organisation said it would stay down for 24 hours.

Instead of encyclopedia articles, visitors to the site saw a stark black-and-white page with the message: "Imagine a world without free knowledge." It carried a link to information about the two congressional bills and details about how to reach lawmakers.

It is the first time the English site has been blacked out. Wikipedia's Italian site came down once briefly to protest an Internet censorship bill put forward by the Berlusconi government. The bill did not advance.

The shutdown adds to a growing body of critics who are speaking out against the legislation. But some editors are so uneasy with the move that they have blacked out their own user profile pages or resigned their administrative rights on the site to protest. Some likened the site's decision to fighting censorship with censorship.

One of the site's own "five pillars" of conduct says that Wikipedia "is written from a neutral point of view." The site strives to "avoid advocacy, and we characterise information and issues rather than debate them."

Wikipedia founder Jimmy Wales argues that the site can maintain neutrality in content even as it takes public positions on issues. "The encyclopedia will always be neutral.The community need not be, not when the encyclopedia is threatened," he tweeted.

The Wikimedia Foundation, which administers the site, announced the blackout late Monday, after polling its community of volunteer contributors and editors and getting responses from 1,800 of them.